Daisy Chained ADG714 Does not Switch ON

Hi,

I have daisy chained 4 ADG714 chips as suggested in figure 8 of the datasheet. I use 10Kohm pull up resistors at each Dout. I want to switch on all of the channels at a given time so my Din is always high ({ 0xFF, 0xFF, 0xFF, 0xFF }). When I want to turn off the switches, I use the reset pin since that is the quickest way to switch off all channels. Right now, I am not using the reset pin because I just want to see if the switches turn ON. 

Here are the signals I generate from a microcontroller: 

zoomed in:

To test my set-up, I connected S1 pin of the first chip to a 1khz, 500mV sinusoid and expected to see that same signal at D1. What I see at D1, is S1/10:

I want to just close all of the 32 channels so that I can see the same signal inputted at the source, at the drain. 

Can you please help me understand what I am doing wrong

Thank you, 

  • Hi,

    Figure 8 of the datasheet shows how to address multiple ADG714 using the ADG739, it is figure 7 that should be used for a daisy chain configuration.

    The timing diagram for the ADG714 is generated using a 1kohm pull up resistor on DOUT so by using a 10k resistor the DOUT ready time will be longer than what is specified so may that is having an impact.

    Could you please provide a scope shots of the DOUT signal?

    Regards,

    Stephen

  • Hi Stephen,

    Sorry, I meant to type figure 7 not figure 8. I am using the configuration in figure 7. Here is my schematic:

    I changed the pull-up resistor to 1Kohm and I still have the same problem. I looked at the signal at Dout of S3 (shown in the schematic above) and it is sitting at 0V. The Din at the other three switches (S4, S5, S6) are also at 0V. They should all be 3V.

    The data is never clocked out of the input shift register. 

  • Ok, I found my problem: it was the RESET bottom.

    When I keep RESET high (3V) at all times, the switches work as expected. 

    The problem now is, I want to open all the switches at a certain time and I wanted to use the RESET bottom to do that since that is the fastest way to open the switches (8ns). But that does not work:

    If I bring RESET low for when I want to open all switches and then bring it high for when I want to close the switches, the switches will always be open. This periodic change in the state of RESET is causing a problem. 

    Would you please let me know what might be happening. 

  • Hi,

    When you pull the /RESET pin low and return it to high all the switches will turn off and remain off until a valid write takes place. This is outlined in page 12 of the datasheet.

    Regards,

    Stephen

  • What would you classify as a valid write? I tried Doing a master SPI transaction where sync is lowered, data is pushed, and sync is released to logic 1 again. This did not work for me even when there were 10k resistors at Do.